Insulated rotogravure backup cylinder

ABSTRACT

A rotogravure backup cylinder having an outer metal surface electrically insulated from its inner metal shaft by a sleeve of nonconductive material.

United States Patent Inventor Jack Bryer Paramus, NJ. Appl, No. 844,508 Fi1ed July 24, 1969 Patented June 1, 1971 Assignees R. Hoe & Co. Inc.

New York, N.Y. Continuation-impart of application Ser. No. 689,145, Dec. 8, 1967, now abandoned.

INSULATED ROTOGRAVURE BACKUP CYLINDER 6 Claims, 3 Drawing Figs.

u.s. Cl 101/153, 101/219,29/123 rm. c1 B411 9/00 FieldofSearch 101/153,

[56] References Cited UNITED STATES PATENTS 528,278 10/1894 Roberts 308/237X 1,152,680 9/1915 Wieselgreen 308/1 1,891,405 12/1932 Ericksson 101/375 2,164,270 6/1939 George 101/153 2,444,880 7/1948 Robinson 29/123 2,520,504 8/1950 Hooper 101/426 2,558,900 7/1951 Hooper 101/219 3,477,369 11/1969 Adamson et a1. 101/153 3,489,082 1/1970 Morris 101/153 Primary Examiner-Robert E. Pulfrey Assistant Examiner-J. Reed Fisher Attorney-Sawyer and Kennedy ABSTRACT: A rotogravure backup cylinder having an outer metal surface electrically insulated from its inner metal shaft by a sleeve of nonconductive material.

Patenfed June 1, 1971 3,581,659

F763 F/G.2

JIf/f 5/9711? IN V EN TOR.

INSULATED ROTOGRAVURE BACKUP CYLINDER REFERENCE This is a continuation-in-part of application Ser. No.

689,145 filed on Dec. 8, 1967, and now abandoned.

BACKGROUND OF THE INVENTION This invention relates to backup cylinders for rotogravure printing presses and more particularly to a backup cylinder which is electrically insulated from the frames of the press unit for use with a gravure system employing electrostatic means for improving of the transfer of ink from the printing cylinder to a traveling web.

In a typical gravure press, as shown for example in US. Pats. No. 3,254,598 and 3,272,122, there is provided a printing cylinder with the matter to be printed etched on its surface, an ink reservoir in which the printing cylinder is partly immersed and rotates so that the ink fills the etched cells of the cylinder, a doctor blade mechanism to wipe the nonprinting (nonetched) surfaces of the printing cylinder clean, an impression roller, usually of a yieldable material such as a rubber, in parallel tangential relationship to the printing cylinder and a backup cylinder for applying counter pressure to the impression roller which is in parallel tangential relationship with the impression roller. The ink which fills the etched cells on the printing cylinder is transferred to the travelling paper web as it passes between the impression roller and the printing cylinder.

The transferability of the ink in the etched cells of the printing cylinder onto the paper has been the subject of much research and study. This transferability of the ink has traditionally depended upon the pressure applied by the impression roller on the printing cylinder. A recent development has improved this transferability by placing an electric charge on the impression roller. The ink is then drawn out of the etched cells and onto the web by electrostatic attraction. Such a system can be more fully understood by referring to the following trade publications: Gravure Research Institute Press Research Report, No. Pl9, Oct. 21, I964; Gravure Research Institute Newsletter, No. 14, July 1966, Pages I I I4; Gravure Magazine, Sept. 1967, pages 303 1.

One of the problems presented by this system is how to place an electrostatic charge on the surface of the impression roller without having it short circuited to ground through the backup cylinder, as this is usually made of steel, having its steel shaft journaled in the side frames of the press unit. One of the proposals for overcoming this problem is to locate the means for applying the charge to the roller directly on the impression roller and placing a coating of insulating material on the surface of the backup cylinder. This proposal will solved the problem of insulating the backup cylinder from the grounded frames, but it has a serious disadvantage in that any insulating coating on the surface of the backup cylinder will eventually wear off and again present the danger of a short circuit to ground. There is also the problem of possible arcing in an explosive operating atmosphere.

An alternative proposal would be to electrically insulatethe .entire backup cylinder by insulating the supporting ball bearings at the journal. This also would not be satisfactory since there would still be the danger of grounding out the circuit should the bearing insulation crack, or because of conductive lubricants which might be used.

It is therefore an object of the present invention to provide a backup cylinder for use with an electrostatic ink transfer system on a rotogravure press without the disadvantages of the prior proposals.

Another object is to provide a backup cylinder having a steel surface for more effective counter pressure action.

A further object is to provide a backup cylinder having a novel construction whereby its outer steel surface is insulated from the side frames of the machine, without having to also insulate the inner shaft therefrom, and therefor the surface is insulated from ground so that any electric charge placed on the impression roller will not be short circuited to ground through the backup cylinder.

Other objects, advantages and features of the present invention will become more apparent from the following detailed description in connection with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings: FIG. I is a side view in partial section of the present inven tion;

FIG. 2 is a section taken along line 22 of FIG. I; and FIG. 3 is a schematic side elevational view of a rotogravure press unit employing an electrostatic ink transfer system.

DESCRIPTION OF THE PRESENT INVENTION Turning to FIG. 3 there is shown a rotogravure press unit employing an electrostatic ink transfer system. A printing cylinder 14 having an etched printing surface 18 is immersed and rotates in an ink reservoir 15. The rotating cylinder picks up the gravure ink 16 which fills the etched cells on the cylinder surface, and the doctor blade device 22 wipes the nonetched surface clean. An impression roller 13, having a surface of conductive rubber and being isolated from the side frames, is mounted tangentially to the printing cylinder 14 and operates to depress the travelling web W against the printing cylinder surface 18 until in contacts the ink in the etched cells so as to transfer the ink to the web as it passes between the impression roller and the printing cylinder. A backup cylinder 10 is also rotatably journaled on ball bearing supports between sliding support blocks 20, 21 of the unit and in parallel tangential relationship to the impression roller 13 for applying counter pressure thereto.

An'electric field of from 500 to 2,000 volts is placed on the impression roller 13 by means of terminal 17.or by any other suitable means such as a generator roller. FIG. 3 shows this field as a positive one, however its polarity can be reversed without affecting the principles of the system. This field will penetrate the paper web W and will assist in transferringthe ink onto the web by electrostatic forces as described in the above-mentioned articles.

The construction of the backup cylinder as provided for in this invention is shown in FIGS. 1 and 2. By the nature of the system described above it is necessary to electrically insulate the outer surface of the backup cylinder from the side frames so that the electric charge will not be grounded out or dissipated. This has been accomplished, without having to also insulate the steel shaft 11 from the frames, by placing a sleeve of insulating material 12 between the shaft 11 and the outer steel surface 10. While any nonconducting material havinga proper dielectric constant might be adequate to electrically insulate the outer steel surface of the cylinder from ground, the material must also be of sufficient hardness so as to be capable of withstanding high compressive forces, in the order of magnitude of approximately 16,000 lbs. distributed about the roller, so that the backup cylinder will not lose its effectiveness as a counter pressure cylinder for the impression roller and so that the insulating material will not mechanically breakdown. Accordingly, any material having characteristics which would make it capable of withstanding as much as 2,000 volts without electrically breaking down, and as much as 16,000 lbs. without mechanically breaking down would be adequate. Materials known commercially as laminated phenolics having a cotton, asbestos or linen base have been found to have such characteristics and meet the requirements for the insulating material I2. In particular, it has been found that a laminated phenolic material with a fine weave cotton cloth base, having a manufactures grade number of 1841 (NEMA grade LE) is preferred. This material has a tensil strength of l0,000 lbs. per square inch and a compressive strength of 25,000 lbs. per square inch. This is more than adequate to withstand the forces which are applied to the backup roller as specified above, provided the insulating sleeve 12 has a wall thickness of from between 0.031 inches to 2.0 inches. With the insulating sleeve 12 having a thickness of approximately from one-half inch to l inch it will be understood that this material is quite sufficient to withstand the mechanical force applied to the backup roller.

The particular insulating material found to be most acceptable, as specified above, is known to have a dielectric constant of from 4.3 to 4.6, depending on atmospheric conditions, and a dielectric strength of from 300 to 500 volts per mil (short time application). With the sleeve of insulating material 12 having the desired thickness averaging approximately three quarters of an inch it will be capable of withstanding approximately from 225 kv. to 350 kv. over a short time application without losing any of its electrical insulating property. The amount of voltage which this material at from one-half inch to 1 inch thickness is capable of resisting without electrical breakdown over a long time application is a good deal less than that stated above for the short time application, but nonetheless is well above the l,000 to 1,200 volts usually applied in this type of system, and in face is well above the 2,000 volt maximum which may be applied in this type of system.

Other materials having similar electrical and mechanical characteristics as those specified for the preferred material discussed above, will be equally sufficient for use as the insulating sleeve 12.

The insulating sleeve 12 need not run along the entire length of the inner shaft but need only be of sufficient length to isolate the outer steel sleeve from the shaft. With the outer sleeve having a hollowed out section as shown in FlG. l the insulating sleeve 12 can be broken into two short sections each of approximately 5.5 inches long with a wall thickness being tapered from one-half inch at the thinnest point to 1 inch at the thickest end and press fitted onto the ends of the shaft 11. The insulating sleeves are secured in place to prevent slip by means of plates 30 and screws 31. With the insulating material broken into sections of 5.5 inches each, it will be necessary that each section be capable of withstanding approximately 1,450 lbs. per axial inch, the material specified above being capable of meeting these requirements.

As can be seen from the above description and accompanying drawings a backup cylinder having an outer steel surface insulated from its inner shaft by a material having the mechanical and electrical characteristics described herein has been provided which can be used on a rotogravure press unit having an electrostatic ink transfer system, without presenting the danger of shorting out the circuit or dissipating the charge. The cylinder can be mounted in regular bearing supports at the frames and it will contact the impression roller with a steel surface to insure proper counter pressure action.

While the invention has been described and illustrated with respect to a certain preferred embodiment which gives satisfactory results, it will be understood by those skilled in the art after understanding the purpose of the invention that various other changes and modifications may be made without departing from the spirit and scope of the invention and it's therefore intended in the appended claims to cover all such changes and modifications.

lelaim:

1. In a rotogravure printing press the combination comprising a pair of side frames, an ink reservoir, a printing cylinder having an etched printing surface rotatably mounted between said side frames and partially immersed in said ink reservoir, a doctor mechanism mounted adjacent to said printing cylinder for wiping said surface clean of excess ink, a pair of sliding support blocks mounted between the side frames, an impression roller mounted between said sliding support blocks electrically isolated therefrom and in parallel tangential relationship to said printing cylinder for exerting pressure on a paper web travelling between said impression roller and said printing cylinder so that the ink can be transferred from the etched cells of said printing cylinder surface to the web, means for applying an electrostatic field to the surface of said impression roller for electrostatically assisting in drawin the ink out of the etched cells of said printmg cylinder an onto said web,

and a backup cylinder for applying counter pressure to said impression roller journaled in said sliding support blocks and in parallel tangential relationship to said impression roller comprising an inner steel shaft, an outer steel sleeve surrounding said shaft, and a sleeve of electrically insulating material separating said inner steel shaft from said outer steel sleeve, whereby said outer steel sleeve is in contact with said impression roller and electrically insulated from ground so that said electric field on said impression roller is prevented from shorting to ground through said backup cylinder.

2. The rotogravure printing press according to claim 1 wherein said sleeve of insulating material is a laminated phenolic with a fine weave cotton cloth base.

3. The rotogravure printing press according to claim 2 wherein said sleeve of insulating material is tapered having a thickness of from one-half inch at its thinnest point to one inch at its thickest point so as to resist an electrical force of 2,000 volts and a mechanical force of 1,450 pounds per axial inch.

4. The rotogravure printing press according to claim 3 wherein said insulating material has a dielectric constant of from between 4.3 and 4.6.

5. The rotogravure printing press according to claim 4 wherein said outer steel sleeve of said backup cylinder has an annular cavity on its inner surface, and said insulating sleeve is split into two sections having a length of approximately 5.5 inches each, each of said sections being fitted onto said inner shaft on either side of said cavity so that said sleeve is electrically insulated from said inner shaft.

6. A backup cylinder for use in a rotogravure printing press unit employing means for electrostatically transferring ink from an etched printing cylinder to a web travelling between said printing cylinder and an impression roller including means for applying approximately between 1,000 and l,200 volts on said impression roller, said backup cylinder having a compressive force of approximately 16,000 pounds applied thereto and comprising an inner steel shaft, an outer steel sleeve surrounding said shaft, said outer sleeve having an annular cavity on its inner surface, and a pair of sleeves each of approximately 5.5 inches in length and averaging approximately three-quarter inch thick and being of a laminated phenolic with a fine weave cotton cloth base, said material to be press fitted onto said shaft inbetween said shaft and said outer steel sleeve for withstanding said electrical and mechanical forces for electrically insulating said outer sleeve from said inner steel shaft.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,5 59 Dated June 1, 1971 Inventor(s) Jack Bryer It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Page I, Item [73] under Assignees, change "R. Hoe 8c 60. Inc. New York, N.Y." to -Wood Industries, Inc.

Plainfield, N.J.--.

Signed and sealed this 21st day of March 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents 

1. In a rotogravure printing press the combination comprising a pair of side frames, an ink reservoir, a printing cylinder having an etched printing surface rotatably mounted between said side frames and partially immersed in said ink reservoir, a doctor mechanism mounted adjacent to said printing cylinder for wiping said surface clean of excess ink, a pair of sliding support blocks mounted between the side frames, an impression roller mounted between said sliding support blocks electrically isolated therefrom and in parallel tangential relationship to said printing cylinder for exerting pressure on a paper web travelling between said impression roller and said printing cylinder so that the ink can be transferred from the etched cells of said printing cylinder surface to the web, means for applying an electrostatic field to the surface of said impression roller for electrostatically assisting in drawing the ink out of the etched cells of said printing cylinder and onto said web, and a backup cylinder for applying counter pressure to said impression roller journaled in said sliding support blocks and in parallel tangential relationship to said impression roller comprising an inner steel shaft, an outer steel sleeve surrounding said shaft, and a sleeve of electrically insulating material separating said inner steel shaft from said outer steel sleeve, whereby said outer steel sleeve is in contact with said impression roller and electrically insulated from ground so that said electric field on said impression roller is prevented from shorting to ground through said backup cylinder.
 2. The rotogravure printing press according to claim 1 wherein said sleeve of insulating material is a laminated phenolic with a fine weave cotton cloth base.
 3. The rotogravure printing press according to claim 2 wherein said sleeve of insulating material is tapered having a thickness of from one-half inch at its thinnest point to one inch at its thickest point so as to resist an electrical force of 2,000 volts and a mechanical force of 1,450 pounds per axial inch.
 4. The rotogravure printing press according to claim 3 wherein said insulating material has a dielectric constant of from between 4.3 and 4.6.
 5. The rotogravure printing press according to claim 4 wherein said outer steel sleeve of said backup cylinder has an annular cavity on its inner surface, and said insulating sleeve is split into two sections having a length of approximately 5.5 inches each, each of said sections being fitted onto said inner shaft on either side of said cavity so that said sleeve is electrically insulated from said inner shaft.
 6. A backup cylinder for use in a rotogravure printing press unit employing means for electrostatically transferring ink from an etched printing cylinder to a web travelling between said printing cylinder and an impression roller including means for applying approximately between 1,000 and 1,200 volts on said impression roller, said backup cylinder having a compressive force of approximately 16,000 pounds applied thereto and comprising an inner steel shaft, an outer steel sleeve surrounding said shaft, said outer sleeve having an annular cavity on its inner surface, and a pair of sleeves each of approximately 5.5 inches in length and averaging approximately three-quarter inCh thick and being of a laminated phenolic with a fine weave cotton cloth base, said material to be press fitted onto said shaft inbetween said shaft and said outer steel sleeve for withstanding said electrical and mechanical forces for electrically insulating said outer sleeve from said inner steel shaft. 